SummaryMicroemulsion electrokinetic capillary chromatography (MEEKC) is similar to micellar electrokinetic chromatography (MEKC) in that it separates neutral solutes based on their chromatographic retention factors. In MEEKC solutes partition bek, veen the aqueous phase and oil droplets, which are moving through the solution. The background to MEEKC is described including novel approaches to method development and optimisation. In this case water-immiscible octane forms minute oil droplets that are coated with SDS and butan-1-ok The effects were evaluated using a test-mixture containing nine components of insoluble and soluble acids, bases and neutrals. Selectivity has been adjusted by use of a large number of factors including organic solvent, co-su rfactant, urea, temperature, cyclodextrins, ion-pair reagent. Previous reports on the selectivity in MEEKC have concentrated only on neutral solutes. Separation selectivity was drastically changed with addition of alcohol such as butan-l-ol, propan-2-ol, cyclodextrin or using a low pH buffer. Microemulsion preparation process or filtration of the buffer did not affect the separation. The separation was largely unaffected by the use of methanol or acetonitrile, surfactant concentration, buffer type, oil type, sample diluent or type of the counter-ion. Migration times were dramatically altered with the use of ion-pair reagent and buffer concentration. It was also demonstrated that temperature variations alter the migration time but not the selectivity.

Microemulsion electrokinetic chromatography (MEEKC) is an electrodriven separation technique. Separations are generally achieved using microemulsions consisting of surfactant-coated nanometer-sized oil droplets suspended in aqueous buffer. A cosurfactant such as a short-chain alcohol is generally used to stabilize the microemulsion. This review summarizes the various microemulsion types and compositions that have been used in MEEKC. The effects of key-operating variables such as surfactant type and concentration, cosurfactant type and concentration, buffer pH and type, oil type and concentration, use of organic solvent and cyclodextrin additions, and temperature are described. Specific examples of water-in-oil microemulsions and chirally selective separations are also covered.

No abstract

In previous reports of microemulsion electrokinetic chromatography (MEEKC), analysis times were typically in the order of 10 min as high-ionic strength buffers were used. These buffers produced high currents which limit the voltages which can be applied, therefore, analysis times could not be reduced. The primary cause of the high-ionic strength is the relatively high concentrations of surfactants required to form the microemulsion. The surfactant concentration can be lower when using an oil with a smaller surface tension. This preliminary study showed that migration times in MEEKC can be reduced to below 1 min by using a combination of an optimum microemulsion composition, high voltage, high temperature, short capillaries by injecting via the "short end", or by simultaneously applying pressure and voltage. Long injection sequences and quantitation were found to be possible with minimum buffer depletion effects.